Objective  To search the DNA sequences specific to virulent strain of Streptococcus mutans in the public database and explore new genes or new functions of

already known genes from Streptococcus mutans of serotype c and suppose their functions. Methods  Thirty-one DNA fragments unique to virulent strain of Streptococcus mutans were sequenced. The sequences of these presumptive virulence DNA fragments were subjected to search through software BLASTn and BLASTx in public database, and their putative biological functions were analyzed. Results  Two clones were picked repeatedly. The size of the remaining DNA fragments ranged from 113  bp to 776 bp. The average G+C content was 38.59%, similar to that of the gene-coding sequences in Streptococcus mutans strain UA159 whose genome sequences  were just complete. Of the twenty-nine DNA fragments, five potentially represented new DNA fragments in Streptococcus mutans, thus registered and obtained their gene′ s accession number in GenBank. The remaining DNA fragments showed high homology to known genes of Streptococcus mutans strain UA159. Their predicted  functions of these fragments were associated to bacterial signal transduction, transcriptional regulation, stress-damage repair, biochemical metabolism, outer  membrane protein synthesis, adhesion on tooth surface and hypothetical proteins. Conclusion  The gene analysis, identification and functional forecasting were carried  out through bioinformatics associated software and database to find out new genes and new functions of known genes, and to supply the groundwork for researches in  gene functions.